Heretofore, methyl methacrylate polymers, copolymers of methyl methacrylate with other vinyl compounds, etc. have been used as the dental bonding agents. However, none of these materials have been found to show sufficient adhesion force with respect to dentin. For that reason, procedures such as acid etching of teeth have been relied upon. However, there have arisen the problems of complicating the treatment of teeth, acidifying dentin, etc.